Pulsed Eddy Current is an electromagnetic method to determine wall thickness of electrical conductors. Pulsed eddy currents are eddy currents generated by a pulsed electromagnetic field. Similar to sinusoidal eddy currents, induced pulsed eddy currents are modified by any local variation in the material properties. The pulse is characterized by its duration (T), which enables to generate induced currents with a very high intensity. The time interval between two measurements is linked to the material thickness. The transmission signal from the probe shows a very broad spectrum of frequencies. The received signal also has a frequency (or time) spectrum, the analysis of which provides information coming from different depths in the material.
Working Principle
The PEC instrument probe is placed against the metal weather sheeting of an insulation pipe or vessel. A magnetic field is created by an electrical current in the transmitting coil of the probe. This field penetrates through the weather sheeting and magnetises the pipe wall. The electrical current in the transmission coil is switched off, causing a sudden drop in the magnetic field. As a result of electromagnetic induction, eddy currents will be generated in the pipe wall. The eddy currents diffuse inwards and decrease in strength. The decrease of eddy currents is monitored by the PEC probe and is used to determine the wall thickness.
Reference codes and standards
ISO 20669
Applications of PECT
Corrosion under insulation
Corrosion under fireproofing
Flow accelerated corrosion
Repair wraps
Under water inspection
Strengths of PECT
No need of direct contact for inspection
No need of surface preparation for inspection
Inspection can done on materials with wide temperature range (-100 oC to 550 oC)
PEC readings have good reproducibility
Limitations of PECT
PECT is suitable only for general wall loss, isolated pitting cannot be detected.
PEC wall thickness readings are relative values, showing variations in wall thickness on the object being inspected.
PEC readings depend on the electromagnetic properties of the test specimen.
PEC readings are affected by nearby nozzles, welds and support structures.
